Regulating solvation structure in gel polymer electrolytes with covalent organic frameworks for lithium metal batteries

Stable and safe Li metal anodes are urgent demands for high-energy-density lithium metal batteries (LMBs). The safety concern of LMBs roots in the intrinsic high reactivity of the solvent sheath with Li metal, and the solvent-oriented fragile solid electrolyte interphase (SEI) causes the continuation of malignant reaction and Li dendrite growth. The SEI composition is closely related to the solvation structure of electrolytes. Furthermore, it is also necessary to alleviate the leakage of liquid electrolytes. Herein, regulating solvation structure by the covalent organic framework (COF) in gel polymer electrolyte (GPE) prepared with a one-step radiation method is proposed to achieve superior cycle performance and leakage-free safety in batteries. The COF with a unique channel structure and abundant lithophilic groups of amino and aldehyde (TpPa-2) exists in strong interfacial interaction with solvated Li+ and thus interferes with Li+-solvent coordination. The TpPa-2 modified GPE with increased intimate ion pairs results in the construction of an anion-derived, LiF-rich SEI to regulate Li plating/stripping. The resultant LiFePO4(LFP)//Li coin cell demonstrates superior capacity retention (75%, 1000 cycles) at 0.5 C. Furthermore, the assembled LFP//Li pouch cell displays excellent flexibility and the capability of resisting LE leakage. This study demonstrates an effective strategy of offering dependable COF-modified GPE to develop LMBs and provides a new horizon into the character of the COF in the long-term cycle performance of LMBs.